A host calculator is connected to a storage device via a network. The storage device of this kind includes, for example, a plurality of hard disk drives (“HDDs”) as a memory device that memorizes data. When data is stored in the storage device, processing of reducing the amount of data is performed to reduce the cost required for a memory medium. To reduce the amount of data, file compression processing or deduplication processing is used. The file compression processing reduces the data capacity by contracting data segments of the same content in one file. On the other hand, the deduplication processing reduces the total data capacity of a file system or storage system by contracting data segments of the same content detected between files, in addition to one file.
In the following, a data segment of a unit for deduplication processing is referred to as “chunk.” Also, data collecting a plurality of chunks is referred to as “container.” Also, logically-collected data of a unit to be stored in a memory device is referred to as “content.” The content includes a file aggregating normal files such as an archive file, a backup file and a virtual volume file, in addition to a normal file. Chunks subjected to deduplication processing are stored in a memory device in a container unit.
In a container, a predetermined chunk number or predetermined capacity is set. Chunks generated from one or two or more contents are collected until a container is filled, and then written in a memory device in a container unit. After the writing, a container index table showing a chunk storage position in a container is generated depending on each container. At this time, a chunk index table showing which chunk is stored in which container, is generated too. For example, when backup data over multiple generations is deduplicated and stored in a memory device, respective containers are prepared for the generations depending on the backup timing, and the generation backup data is stored in each container (for example, see Patent Literature 1).